The present subject matter relates generally to radio transmission techniques and more particularly to reducing leakage in direct conversion radio transmitters.
Wireless communication devices have become ubiquitous in today's society. The heart of every wireless communication device consists of a transmitter and a receiver to transmit and receive radio signals. A radio frequency (RF) transmitter converts low frequency signals (e.g., in the 100 kHz-4 MHz range), to a desired RF frequency band (e.g., in the 1.9-2.0 GHz range) that may then be transmitted through various communication channels. The process of transforming the low frequency signals to an RF signal is referred to as mixing or “upconversion.” This mixing is often performed by providing the frequencies to be mixed to a non-linear mixing device (e.g., a diode), where the sums and differences of these frequencies are generated.
Conventionally, the low frequency signals are upconverted to an intermediate frequency (IF) then upconverted again to an RF band using heterodyne techniques. More recently however, direct conversion transmitters directly convert the low frequency signals to higher frequency RF band signals without first converting to an IF. In this architecture, the low frequency signal is mixed with a frequency from a local oscillator (LO) that has a substantially higher frequency. Direct conversion architectures are advantageous in that fewer components are needed, thereby reducing overall system cost. However, although the direct conversion transmitter design allows a reduction in the number of components, imperfections in transmitter circuitry result in signals from the LO undesirably leaking into other portions of the transmitter circuitry. This leakage can be especially problematic at low output power.
Accordingly, methods and apparatuses for reducing the amount of leakage are desirable.